Carotenoids are yellow, red and orange pigments that are widely distributed in nature. Although specific carotenoids have been identified in various fruits and vegetables, bird feathers, egg-yolk, poultry skin, crustaceans and macular eye region, they are especially abundant in marigold petals, corn and leafy vegetables. The correlation between dietary carotenoids and carotenoids found in human serum and plasma indicate that only selected groups of carotenoids make their way into the human blood stream to exert their effect.
Carotenoids absorb light in the 400-500 nm region of the visible spectrum. This physical characteristic imparts the yellow/red color to the pigments. Carotenoids contain a conjugated backbone composed of isoprene units, which are usually inverted at the center of the molecule, imparting symmetry. Changes in geometrical configuration about the double bonds result in the existence of many cis- and trans-isomers. Mammalian species do not synthesize carotenoids and therefore these have to be obtained from dietary sources such as fruits, vegetables and egg yolks. In the recent years, carotenoids have been attributed several health benefits, which include prevention and or protection against serious health disorders.
Carotenoids are non-polar compounds classified into two sub-classes, namely more polar compounds called xanthophylls or oxy-carotenoids and non-polar hydrocarbon carotenes like [beta]-carotene, lycopene, etc. Both the sub-classes have at least nine conjugated double bonds responsible for the characteristic color of the carotenoids. Xanthophylls have ring structures at the end of the conjugated double bond chain with polar functionalities, such as hydroxyl or keto groups. Examples of xanthophylls include lutein, zeaxanthin, capsanthin, canthaxanthin, J3-cryptoxanthin, astaxanthin, etc. As natural colorants and also for their role in human health, xanthophylls containing lutein and zeaxanthin have attracted the renewed attention of scientists and researchers in the biomedical, chemical and nutritional field in recent years.
Lutein and zeaxanthin contribute to yellow and orange-yellow color respectively. Lutein and zeaxanthin can be present in plant material in free form (non-esterified) and also as esters. Lutein is present in green leafy vegetables like spinach, kale and broccoli in the free form while fruits like mango, orange, papaya, red paprika, algae and yellow corn. These sources generally contain lutein in the form of its esters etc. Lutein is also present in the blood stream and various tissues in human body and particularly the macula, lens and retina of the eye.
Marigold (Tagetes erecta) flower petals are a rich source of lutein in its esterified form. The ester portion(s) are fatty acids. Dried marigold flowers contain approximately 1-1.6% carotenoids by weight and lutein esters content accounts for 90% of the total carotenoids. The xanthophyll fatty acid esters composition in marigold oleoresin chiefly consists of lutein in its ester form as di-palmitate, myristate-palmitate, palmitate-stearate, dimyristate and monoesters.
Lutein obtained by the hydrolysis of lutein esters from marigold have been found to be identical to the lutein found in fruits, vegetables and in human plasma and the macular region. After absorption, the human body cannot distinguish the source of lutein. Therefore, a widely cultivated and commercially processed raw material like marigold, which is already used by the food and feed industry, is an attractive source for lutein in view of abundant availability and cost considerations.
Essentially, lutein esters and lutein in the free form are commercially important nutraceuticals obtained from marigold flowers. Dried flowers are used for obtaining marigold extract or oleoresin. By subjecting the extract/oleoresin to saponification, xanthophylls in the free form are obtained. The resultant alkali salts of fatty acids obtained from the saponification are removed and the xanthophyll containing mixture of lutein and zeaxanthin purified further.
In the fresh marigold flowers, lutein esters exist in trans-isomeric form, whereas exposure to heat, light, oxygen, acid, etc. catalyses isomerization from trans- to cis-lutein geometric isomeric forms. As a nutraceutical and food additive, the trans-isomeric form of lutein is preferred because of better bio-availability and deeper yellow color compared to the corresponding cis-isomeric form.
In virtually all the processes described in the literature, including patents, invariably the first step of isolation and purification of the xanthophylls, such as lutein, is the aqueous saponification of oleoresin (specifically marigold) using an alcoholic and/or aqueous alkali preferably KOH. The saponification steps in these processes generally employ the use of water in the process. The processes additionally involve extracting and re extracting with solvents such as tetrahydrofuran or halogenated solvents. Additionally, many of the processes utilize elevated temperatures, such as about 70° C., that can degrade the material or isomerizes the olefinic bonds. Therefore these processes are inappropriate for industrial scale-up operations due to high cost & toxicological considerations.
Therefore, a need exists for a process to prepare solid xanthophylls that eliminates the use of water, high temperatures for saponification, and or reduced amounts of solvents.